Modular oil-based sludge separation and treatment system

ABSTRACT

A modular apparatus having certain processing equipment mounted on portable skids that are adaptable and versatile to permit customized arrangement for oil-recovery processing of a wide range of oil-base sludge compositions in a cost-efficient manner. In one aspect, the invention is directed to a modular apparatus optimally configured for oil recovery of sludge having a high concentration of low density solids, wherein the apparatus may include a pumping skid, a shaker skid, a heating skid, a chemical skid, a phase separator skid, a gas purification skid, a decanter skid, and an oil purification skid. In another aspect, the invention is directed to a modular apparatus optimally configured for oil recovery of sludge having a high concentration of high density solids, wherein the apparatus may include a pumping skid, a shaker skid, a heating skid, a first chemical skid, a decanter skid, a second chemical skid, a phase separator skid, a gas purification skid, and an oil purification skid. In still another aspect, the invention is directed to a modular apparatus optimally configured for oil recovery of sludge having a very low solids content, wherein the apparatus may include a pumping skid, a shaker skid, a heating skid, a chemical skid, a phase separator skid, a gas purification skid, and an oil purification skid.

BACKGROUND OF INVENTION

Oil-based sludges of various types and consistencies are commonlygenerated as waste streams during oil or other hydrocarbon productionprocesses. These sludges arise during well tests and initial production,as a by-product waste stream of hydrocarbon production, and as tankbottom sediments. The basic components of sludges are hydrocarbon oilsof various consistencies, water, and solids of an inorganic and organicnature. Oil-based sludge typically refers to a complex water-in-oilemulsion stabilized by salts of organic compounds and fine solids. Theoil phase contains a complex mixture of hydrocarbons of variousconsistencies including waxes and asphaltenes which may be solid orsemi-solid at ambient temperature.

The chemistries of oil-based sludges and the relative proportions of theoil, water, and solid phases of sludges vary greatly and can change overtime. To dispose of the waste, sludge is often stored in open pits whereit may be left for considerable time before being treated. During suchaging periods, the sludge or “pit sludge” undergoes overall chemicalcomposition changes due to the effects of weathering, including:volatilization of lighter hydrocarbons; temperature induced crosslinkingof hydrocarbons; addition of rain water; and, invariably, theintroduction of a variety of other contaminants, particulates, anddebris. In addition to a variable complex chemistry, oil-based sludgetypically has a high solids content. Sludge solids normally include bothhigh density and low density solids. High density solids, i.e., highgravity solids, may be large solids introduced into the drilling fluidduring the drilling of a formation (e.g. formation solids, drill bits,etc.) or other solids that are relatively dense such as barite orhermatite. While low density solids, i.e., low gravity solids, are thosesolids within the sludge that have a lower density or are relativelysmall fine solids (e.g., entrained solids such as sand).

Currently, treatment of sludge is a major operational cost forproducers. Sludge is collected, stored, and then disposed of in tanks ordelivered to a sludge pit. One challenge of sludge treating systems isthat the recovery of marketable oil from the sludge is generally notcost-effective and thus not commercially viable. Due to wide variabilityin sludge composition, different sludge processing systems may be neededto optimize the processing of sludge for recovering oil of sufficientquality in a cost efficient manner. The quality of oil is frequentlycharacterized by its Basic Sediment and Water (BS&W) content, in vol. %.The current marketable BS&W of recovered oil is less than about 2 vol.%. Furthermore, it is desirable to treat pit sludge to reduce the riskof contamination of the surrounding pit area, in accordance withincreasingly strict environmental regulations, as well as decrease theoverall waste volume, and ultimately to permit pit closure.

SUMMARY

The present invention is generally directed to a modular oil-basedsludge separation and treatment apparatus that is easily adapted toprovide processing flexibility in order to ensure quality oil recoveryfrom oil-based sludge in an efficient and cost-effective manner. Themodular approach allows the configuration of processing equipment to beadapted to the oil-recovery processing requirements of the particularoil-based sludge composition. Providing a customizable apparatusmaximizes the quantity and quality of the recovered oil while minimizingthe processing time and cost to the operator.

It is an objective of the present invention to provide a modularapparatus having certain processing equipment mounted on portable skidsthat are adaptable and versatile to permit customized arrangement foroil-recovery processing of a wide range of oil-base sludge compositionsin a cost-efficient manner.

In one aspect, the invention is directed to a modular apparatus forrecovering oil from oil-based sludge having a high concentration of lowdensity solids. The modular apparatus includes: a pumping skid having apump operable to homogenize an oil-based sludge; a shaker skid having ascreen that removes particulates from the oil-based sludge as the sludgetraverses the screen to form a debris-free sludge; a heating skidshaving a heat exchanger operable to heat the debris-free sludge as: thedebris-free sludge flows through the heat exchanger to form a heatedsludge; a chemical skid having at least one chemical injection mixeroperable to inject a chemical into the heated sludge and mix thechemical with the heated sludge to form a chemically-treated sludge; aphase separator skid having a three-phase separator operable to separatethe phases of the chemically-treated sludge to form a first solidscomponent stream, a first water component stream, a first oil componentstream, and a first gas component stream; a decanter skid having adecanter centrifuge operable to remove solids from the first oilcomponent stream to form a second solids component stream and a secondoil component stream; and an oil purification skid having a disk stackcentrifuge operable to remove water and solids from the second oilcomponent stream to form a third solids component stream, a second watercomponent stream, and a third oil component stream.

In another aspect, the invention is directed to a modular apparatus forrecovering oil from oil-based sludge having a high concentration of highdensity solids. The modular apparatus includes: a pumping skid: having apump operable to homogenize an oil-based sludge; a shaker skid having ascreen that removes particulates from the oil-based sludge as the sludgetraverses the screen to form a debris-free sludge, a heating skid havinga heat exchanger operable to heat the debris-free sludge as thedebris-free sludge flows through the heat exchanger to form a heatedsludge; a first chemical skid having at least one chemical injectionmixer operable to inject a chemical into the heated sludge and mix thechemical with the heated sludge to form a first chemically-treatedsludge: a decanter skid having a decanter centrifuge operable to removesolids from the first chemically-treated sludge to form a first solidscomponent stream and a decanter-processed sludge; a second chemical skidhaving at least one chemical injection mixer operable to inject achemical into the decanter-processed sludge and mix the chemical withthe decanter-processed sludge to form a second chemically-treatedsludge; a phase separator skid having a three-phase separator operableto separate the phases of the second chemically-treated sludge to form asecond solids component stream, a first water component stream, a firstoil component stream, and a first gas component stream; and an oilpurification skid having a disk stack centrifuge operable to removewater and solids from the first oil component stream to form a thirdsolids component stream, a second water component stream, and a secondoil component stream.

In still another aspect, the invention is directed to a modularapparatus for recovering oil from oil-based sludge having very lowsolids content. The modular apparatus includes: a pumping skid having apump operable to homogenize an oil-based sludge; a shaker skid having ascreen that removes particulates from the oil-based sludge as the sludgetraverses the screen to form a debris-free sludge; a heating skid havinga heat exchanger operable to heat the debris-free sludge as thedebris-fee sludge flows through the heat exchanger to form a heatedsludge; a chemical skid having at least one chemical injection mixeroperable to inject a chemical into the heated sludge and mix thechemical with the heated sludge to form a chemically-treated sludge; aphase separator skid having a three-phase separator operable to separatethe phases of the chemically-treated sludge to form a first solidscomponent stream, a first water component stream, a first oil componentstream, and a first gas component stream; and an oil purification skidhaving a disk stack centrifuge operable to remove water and solids fromthe first oil component stream to form a second solids component stream,a second water component stream, and a second oil component stream.

These and other features are more fully set forth in the followingdescription of preferred or illustrative embodiments of the disclosedand claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobjects of the present invention are attained and can be understood indetail, a more particular description of the invention, brieflysummarized above, may be had by reference to the embodiments thereofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only typical embodimentsof this invention and are therefore not to be considered limiting of itsscope, for the invention may admit to other equally effectiveembodiments.

FIG. 1 is a flow chart depicting a modular skid arrangement optimizedfor recovering the valuable hydrocarbon component of pit sludge having ahigh concentration of low density solids, according to an embodiment ofthe invention;

FIG. 2 is a flow chart depicting another modular skid arrangementoptimized for recovering the valuable hydrocarbon component of pitsludge having a high concentration of high density solids, according toanother embodiment of the invention;

FIG. 3 is a flow chart depicting still another modular skid arrangementoptimized for recovering the valuable hydrocarbon component of pitsludge having very low solids content, according to still anotherembodiment of the invention;

FIGS. 4 and 5 are schematics of an exemplary modular apparatus forseparating and treating an oil-base sludge having a high concentrationof low density solids to recover the valuable hydrocarbon component, inaccordance with the skid arrangement shown in FIG. 1;

FIGS. 4 and 6 are schematics of an exemplary modular apparatus forseparating and treating an oil-base sludge having a high concentrationof high density solids to recover the valuable hydrocarbon component, inaccordance with the skid arrangement shown in FIG. 2; and

FIGS. 4 and 7 are schematics of an exemplary modular apparatus forseparating and treating an oil-base sludge having very low solidscontent to recover the valuable hydrocarbon component, in accordancewith the skid arrangement shown in FIG. 3.

DETAILED DESCRIPTION

The claimed subject matter relates to a modular apparatus having one ofseveral skid arrangements depicted in FIGS. 1-3 for recovering thevaluable hydrocarbon component of oil-based sludges having a widevariability in sludge composition. Depending upon the particular sludgecomposition and its solids content, the skid arrangements of the modularapparatus of the present invention may be easily configured, andre-configured, in order to optimize the separation and purification ofthe recovered oil while minimizing the time and cost to an operator.

According to an embodiment of the invention, FIG. 1 depicts the skidarrangement: of a modular apparatus 100 optimally configured forrecovering the valuable hydrocarbon component of sludge 14 initiallyhaving a high concentration of low density solids, Modular apparatus 100comprises a pumping skid 102, a shaker skid 104, a heating skid 106, achemical skid 108, a phase separator skid 110, a gas purification skid112, a decanter skid 114, and an oil purification skid 116. Each of theskids 102-116 are described in more detail in the description thatfollows with respect to the modular apparatus 100 schematicallyillustrated in FIGS. 4 and 5.

As illustrated in FIGS. 4 and 5S modular apparatus 100 processes pitsludge through the pumping skid 102, the shaker skid 104, the heatingskid 106, the chemical skid 108, the phase separator skid 110, the gaspurification skid 112 the decanter skid 114, and the oil purificationskid 116. Referring to FIG. 4, the pumping skid 102 includes a hydraulicsubmersible sludge pump 122 that homogenizes a pit sludge 10 containedin a pit 12 and then pumps a homogenized sludge 14 to the shaker skid104. The pump 122 may be mounted on a hydraulic arm in order to reachinner areas of the pit 12. During ageing, the pit sludge 10 separatesinto basically three layers or phases, wherein the top layer of the pitis an oil-rich phase, the middle layer of the pit sludge 10 is awater-rich phase, and the bottom layer of the pit sludge 10 is asolids-rich phase. The pump 122 forms a homogeneous mixture or slurry ofthe three phases contained within the pit in order to provide agenerally constant feed composition to the remainder of the apparatus100 for processing.

The shaker skid 104 includes a shaker screen 124 and a holding tank 126mounted thereon and within the confines of the area in the skid 104 soas to maintain portability of the skid 104. The shaker screen 124physically separates and removes large particulates such as stones ordebris from the sludge 14. A debris-free sludge 16 exiting the shakerscreen 124 collects in the holding tank 126. Holding tank 126 may beessentially any type of tank that can contain a sufficient amount ofsludge to supply and maintain a constant sludge flow rate to a heatexchanger 130. A first transfer pump 128 in fluid communication with theholding tank 126 transfers the sludge 16 from the holding tank 126 tothe heating skid 106. In a preferred embodiment, the holding tank 126 isan augured V-Tank coupled to the pump 128 which is VFD (variablefrequency driver) controlled in order to automatically provide a steadystate flow rate of the sludge 16 to the heat exchanger 130.

The heating skid 106 has the heat exchanger 130, a steam boiler 132, anda fuel tank 134 mounted thereon and within the confines of the area ofthe skid 106 so as to maintain the portability of the skid 106. Sludge16 is heated to a desired temperature as it travels through the heatexchanger 130. Because oil-based sludges often include waxyhydrocarbons, heating advantageously melts the waxy hydrocarbons intoliquid form and lowers the viscosity of the sludge 16. Also, heatingadvantageously aids in breaking the emulsion (secondary phase) andpromotes phase separation within the sludge 16. Providing heat to theheat exchanger 130 is accomplished by use of the steam boiler 132. Thesteam boiler 132 generates steam and circulates the steam to the heatexchanger 130 via a first steam line 136 and a second steam line 138.The flow rate, pressure, and temperature of the steam entering the heatexchanger 130 via line 136 are controlled so as to provide adequate heattransfer to the sludge 16 as it flows through the heat exchanger 130. Aheated sludge 18, having the desired temperature and viscosity, exitsthe heat exchanger 130 and is subsequently transferred to the chemicalskid 108. In one example, the type of heat exchanger 130 used is aspiral type heat exchanger, wherein sludge 16 flows through the heatexchanger 130 in a path separate from that of the steam, but adjacent toit such that heat from the steam is transferred to the sludge 16. It isunderstood that other types of heat exchangers can be used withoutdeparting from the scope of this invention.

Depending upon the particular sludge composition, the sludge 16 isheated to essentially any temperature sufficient to liquefy the sludge16 and lower its viscosity. When the viscosity is lower, treatmentchemicals may be more easily blended with the heated sludge 18 indownstream processing. Furthermore, when the sludge viscosity is lower,entrained solids are more easily released in downstream processing. Thedesired temperature of the heated sludge 18 and its correspondingrheological profile can be predetermined and optimized using aviscometer, such as an oilfield Fann 35 viscometer available from FannInstrument Co. In one example, sludge 18 is heated to a temperature inthe range from about 65° C. to about 85° C. to sufficiently liquefy thesludge 18 and reduce its viscosity for downstream processing. Morepreferably, sludge 18 is heated to a temperature in the range from about70° C. to about 80° C. Although it is desirable to heat the sludge 16,care should be taken to ensure that the temperature of the heated sludge18 is lower than the flash point temperature of the sludge 16. The flashpoint is that minimum temperature at which there is enough evaporatedfuel in the air to start combustion. The flash point of the sludge 16can be determined by the use of a flash-point measuring device such asthe Pensky Martens Closed Cup according to method ASTM D93B.

Preferably, the fuel tank 134 is co-located on the skid 106 to providefuel to the steam boiler 132 for heating the steam. Optionally, a powersupply (not shown) is provided on the skid 106 to actuate valves (notshown) that regulate the flow rate of the steam through the first andsecond steam lines 136, 138, and also regulate the flow rates of thewater supply and the fuel provided to the steam boiler 132. A controlpanel (not shown) may be co-located on the skid 106 to monitor andautomatically control the valves in order to automate the heatingprocess at the heat exchanger 130. In addition, the boiler 132, flowlines 136, 138, and heat exchanger 130 are preferably thermallyinsulated to better maintain temperature uniformity and control.

Once heated, the sludge 18 is transferred to a chemical skid 108 forchemically altering the sludge 18 to break up the emulsion and promotephase separation. The chemical skid 108 includes a plurality of chemicalinjection mixers 140 a-d and chemical supply tanks 142 a-d mountedthereon and within the confines of the area of the skid 108 so as tomaintain the portability of the skid 108. Chemical addition is typicallyrequired to destabilize the emulsion and change such properties toenhance separation of the water and solids from the sludge 18, as wellas decrease the separation: time required. Each of the chemicalinjection mixers 140 a-d includes a static shear mixer having aninjection point. The injection point introduces a chemical into thesludge 18 while the mixer simultaneously blends the chemical and thesludge 18 under the shearing action of the mixer. The chemical injectionmixer advantageously provides a homogeneous distribution of the chemicalwithin the sludge 18 to aid in its complete and efficient chemicalreaction therein. As depicted in FIG. 5, four chemicals are added to theheated sludge 18 as the sludge is directed through the chemicalinjection mixers 140 a-d. Each of the chemical injection mixers 140 a-dhas a corresponding chemical supply tank 142 a-d for storing thechemicals until they are transferred via chemical lines 144 a-d to themixers 140 a-d for injection into the sludge 18. Once all the chemicalsare introduced and blended into the heated sludge 18, achemically-treated sludge 20 exits the last chemical injection mixer 140d and is subsequently transferred to the phase separator skid 110 forfurther processing.

Depending upon the particular initial sludge 14 composition, a widevariety of chemicals, may be introduced and blended into the sludge 18in order facilitate subsequent processing to separate the solid, water,and oil phases of the chemically treated sludge 20. Suitable chemicalsinclude acids, demulsifiers, wetting agents, surfactants, flocculants,and defoamers. Demulsifiers modify the interfacial tension of theemulsion film to release the water and assist in separating out thewater from the oil. Wetting agents alter the wetability of solidparticles thereby causing the solid particles to become hydrophilicwhich increases the solids affinity for water and causes further breakupof the interfacial emulsion film. Flocculants induce the solids toaggregate and form larger solids to facilitate separation of the solidsin the sludge. In one example, as the heated sludge 18 travels throughthe first injection mixer 140 a, the mixer 140 a injects an acid andblends the acid with the sludge 18 therein in order to neutralizeadsorbed ions present at the interfacial emulsion film of the sludge 18and chemically prepare the sludge 18 for chemical treatment with ademulsifier. Subsequently, the sludge 18 is directed through the secondinjection mixer 140 b wherein a demulsifier is injected and blended intothe sludge 18 to break the interfacial emulsion film for release of thesecondary water phase. The sludge 18 then passes through the thirdinjection mixer 140 c wherein a wetting agent is injected and blendedinto the sludge to alter the affinity of the solids towards the waterphase. Afterwards, the sludge 18 passes through the fourth injectionmixer 140 d wherein a defoamer is injected and blended into the sludgefor the purpose of counteracting surfactants (detergents) present in thesludge that may otherwise undesirably cause foaming. After chemicaltreatment in injection mixers 140 a-d, a chemically-treated sludge 20exits the chemical skid 108 and is ready for subsequent processing. Itshould be noted that the present invention is not intended to be limitedto the use of any particular chemicals, and other chemicals may besubstituted for any of the aforementioned chemicals.

Furthermore, additional chemicals may be incorporated into the sludge 18by providing additional injection mixers (e.g., 140 e-n) on the skid 108such that all the desired chemicals may be introduced into the sludge.For example, a fifth injection mixer (not shown) may be included on skid108 to introduce a pour point suppressant into the sludge 18 in order toextend the fluidity of the sludge to lower temperatures. Because wax inthe sludge can cause issues for pumping and phase separation in terms ofthe high viscosity it imparts and coating of entrained solids, pourpoint suppressants can be added to depress the temperature at which waxmolecules in the oil phase of the sludge 18 solidify, Conversely, inanother example, fewer chemicals may be incorporated into the sludge 18by bypassing one or more of the injection mixers 140 a-d or,alternatively, removing one of more of the mixers 140 a-d from the skid108.

Preferably at least one dosing pump (not shown) in fluid communicationwith each of the chemical injection mixers 140 a-d is used to provide apredetermined quantity of chemical to the injection point of the mixerfor introduction into the sludge 18. The quantity of each of thechemicals introduced into the sludge 18 depends upon the particularinitial sludge composition 14. For example, a dosing pump in fluidcommunication with the second injection mixer 140 b provides demulsifierin the predetermined amount of 2-3% by volume of sludge 18. Althoughessentially any type of dosing pump may be used, in one example each ofthe dosing pumps is a gear pump with a VFD control panel. In addition,preferably, the chemical injection mixers 140 a-d are thermallyinsulated to better maintain the sludge temperature and fluidity.

After chemical treatment, the sludge 20 is directed to the phaseseparator skid 110 for separating the solid, water, oil, and gas phasesof the sludge 20. The phase separator skid 110 includes a surge tank 146and a three-phase separator 148 mounted thereon and within the confinesof the area of the skid 110 so as to maintain the portability of theskid 110. The sludge 20 is fed into the vertically-oriented surge tank146 which separates heavier solids from the sludge 20 and provides acontinuous flow of a liquid portion of the sludge 22 to the three-phaseseparator 148. The surge tank 146 contains an interior plate thatfacilitates the small solids (e.g., solids in suspension) within thesludge 20 to aggregate and form larger solids such that gravity issufficient to separate these heavier solids out of the sludge 20.Separated solids 24 that settle and accumulate in a bottom region of thesurge tank 146 are discharged and directed to a solids receiving tank150. The liquid portion of the sludge 22, which comprises oil, water,gas, and fine solids, is directed to the three-phase separator 148.

The liquid portion of the sludge 22 flows into the three-phase separator148 through an inlet located at one end of the separator 148. Theseparator 148 is designed to separate the phases and flow the separatedphases to their respective outlets. Within the retention section of thethree-phase separator 148, the liquid portion of the sludge 22 separatesinto a water-rich phase 28, an oil-rich phase 30, and a gas phase 44.Furthermore, additional solids 26 that may settle out of the sludge 22and accumulate in a bottom region of the separator 148, primarily as aresult of the re-distribution or separation of the phases, aredischarged and directed to the solids receiving tank 150. The water-richphase 28 is discharged to a water tank 152. The oil-rich phase 30 istransferred to the decanter skid 114 for fine solids removal. The gasphase 44 is directed to the gas purification skid 112 to clean the gasfor release into the atmosphere. One exemplary three-phase separator 148is the Horizontal Longitudinal Flow Separator commercially availablefrom NATCO Group Inc., Houston, Tex. However, the present invention isnot limited to a particular type of surge tank or three-phase separator.In addition, the surge tank 146 and three-phase separator 148 are bothpreferably insulated to better maintain the sludge temperature andfluidity.

The oil-rich phase 30 is transferred to the decanter skid 114 toseparate the fine solids out of the oil-rich phase 30. The decanter skid114 includes a decanter centrifuge 154 and a heating tank 156 mountedthereon and within the confines of the area of the skid 114 so as tomaintain the portability of the skid 114. For the removal of solids, thedecanter centrifuge 154 is particularly useful in reducing the solidscontent in liquids having a solids concentration in excess of about 3vol. % to a solids concentration less than about 2 vol. %. Once theoil-rich phase 30 is fed into the decanter centrifuge 154, centrifugalforce causes suspended solids to separate out of the oil-rich phase 30and coalesce for subsequent removal from the decanter, Solids 32 aredischarged through a solids outlet located in the bottom of the decantercentrifuge 154. At this point in the processing, a decanter-processedoil-rich phase 34 that exits the decanter 154 has a BS&W of less thanabout 2 vol. %. Suitable decanter centrifuges include decantercentrifuges having a rotational speed of 3000 rpm or greater. Exemplarydecanter centrifuges include Model 500 (3000 rpm) and Model 518 (5000rpm) commercially available from M-I L.L.C., Houston, Tex.

After the fine solids removal, the decanter-processed oil-rich phase 34is transferred to the heating tank 156 and optionally heated therein.Because a significant amount of cooling can occur during the variousprior processing steps, since being previously heated in the heatexchanger 130, the oil-rich phase 34 is optionally heated to a desiredtemperature in the heating tank 156 in order to enhance its final phaseseparation and purification during the next processing step at the oilpurification skid 116. The heating tank 156 includes a heating element(e.g., a steam coil) capable of heating the contents of the tank 156.After heating, a heated oil-rich phase 36 is pumped via a secondtransfer pump 158 to the oil purification skid 116 for finalpurification. In one example, the heated oil-rich phase 36 is heated toa temperature in the range from about 65° C. to about 85° C.

The heated oil-rich phase 36 is transferred to the oil purification skid116 for its final purification and recovery of oil therefrom having aBS&W of less than about 1 vol. %. The oil purification skid 116 includesa disk stack centrifuge 160. As depicted in FIG. 5, the heated oil-richphase 36 is fed into the disk stack centrifuge 160 to further purify theoil. The disk stack centrifuge uses a combination of plates (i.e., thedisk stack) and extremely high centrifugal forces to separate the veryfine water emulsion and the ultra-fine solids out of the oil-rich phase36. After separation, a water stream 38, a recovered oil stream 40, andan ultra-fine solids phase 42 are discharged from the centrifuge 160.After final processing in the disk stack centrifuge 160, the recoveredoil stream 40 has a BS&W less than about 1 vol. % and is commerciallymarketable. Exemplary disk stack centrifuges are commercially availablefrom Alfa Lavel Inc., Richmond, Va.

The gas phase 44 is transferred to the gas purification skid 112 wherethe gas phase 44 is treated to remove volatile organic compounds (VOCs)prior to discharge into the environment. The gas purification skid 112preferably includes a free water knockout pot 162, at least one mistimpinger 166, and at least one activated carbon filter 168 mountedthereon and within the confines of the area of the skid 112 so as tomaintain the portability of the skid 112. A VFD-controlled vacuum blower164 attached to the knockout pot 162 is used to draw the gas phase 44from a gas vent located in an upper side of the three-phase separator148 through the knockout pot 162 filled with water. The gas phase 44enters a gas inlet located near the bottom of the knockout pot 162, andhydrocarbons in the gas phase 44 adhere to the water as the gas travelsupwardly through the pot 162. Water in the knockout pot 162 isperiodically emptied into a liquid waste disposal and replaced withfresh water. Because the exiting gas is saturated with water, a wet-gas46 that exits a gas outlet near the top of the knockout pot 162 isdirected through at least one mist impinger 166 to remove water from thegas 46 and provide a dry gas 48. The dry gas 48 that exits the at leastone mist impinger 166 is then transferred to an activated carbon filter168 to remove contaminants (e.g., remaining VOCs) therefrom in order toensure a gas 50 that meets the environmental regulatory standards forrelease to the atmosphere. In one example, as depicted in FIG. 5, theknockout pot 162 removes hydrocarbons from the gas phase 44, andafterwards the exiting wet-gas 46 is directed through two mist impingers166 to adequately dry the gas prior to directing the dry gas 48 throughone or more activated carbon filters 168. When the activated carbonfilter 168 becomes exhausted, it may be treated to reactivate the carbonor, alternatively, may be disposed of according to appropriateregulatory procedures.

According to another embodiment of the invention, FIG. 2 depicts theskid arrangement of a modular apparatus 200 optimally configured forrecovering the valuable hydrocarbon component of sludge 14 initiallyhaving a high concentration of high density solids. In FIG. 2 the samereference numerals are used to indicate the same skids as thosepreviously described with respect to the apparatus 100 depicted inFIG. 1. Modular apparatus 200 comprises the pumping skid 1025 the shakerskid 104, the heating skid 106, a first chemical skid 118, the decanterskid 114, a second chemical skid 120, the phase separator skid 110, thegas purification skid 112, and the oil purification skid 116. In thisembodiment, two chemical skids 118, 120 are utilized with the decanterskid 114 positioned between the chemical skids 118, 120. For sludge 14initially having a high concentration of high density solids, it ispreferable to remove solids from the sludge using a decanter centrifugeprior to delivery of all the chemicals during the chemical treatment ofthe sludge. Skids 118 and 120 are described in more detail in thedescription that follows with respect to the modular apparatus 200schematically illustrated in FIGS. 4 and 6.

Illustrated in FIGS. 4 and 6, modular apparatus 200 processes pit sludgethrough the pumping skid 102, the shaker skid 104, the heating skid 106,the first chemical skid 118, the decanter skid 114, the second chemicalskid 120, the phase separator skid 110, the gas purification skid 112,and the oil purification skid 116. As previously described with respectto FIG. 4 the modular apparatus 200 processes pit sludge 10 through thepumping skid 102, the shaker skid 104, and the heating skid 106 toprovide a heated sludge 18.

Referring now to FIG. 6, the heated sludge 18 is transferred to thefirst chemical skid 118 for chemically altering the sludge 18 to breakup the emulsion and promote solids separation. In FIG. 6 the samereference numerals are used to indicate the same features as thosepreviously described with respect to apparatus 100 depicted in FIG. 5.The chemical skid 118 includes a plurality of chemical injection mixers140 a, 140 b and chemical supply tanks 142 a, 142 b mounted thereon andwithin the confines of the area of the skid 118 so as to maintain theportability of the skid 118. Chemical addition is typically required todestabilize the emulsion and change such properties to facilitateseparation of the solids from the sludge 18 and decrease the separationtime required. Each of the chemical injection mixers 140 a, 140 bincludes a static shear mixer having an injection point for introducinga chemical into the sludge 18 while the mixer simultaneously blends thechemical and the sludge 18 under the shearing action of the mixer. Asillustrated in FIG. 6, two chemicals are added to the heated sludge 18as the sludge is directed through the chemical injection mixers 140 a,140 b. Chemical supply tanks 142 a, 142 b store the chemicals until theyare transferred via chemical lines 144 a, 144 b to the mixers 140 a, 140b for injection into the sludge 18. Preferably at least one dosing pump(not shown) in fluid communication with each of the chemical injectionmixers 140 a, 140 b is used to provide a predetermined quantity ofchemical to the injection point of the mixer for introduction into thesludge 18. In addition the chemical injection mixers 140 a, 140 b arepreferably insulated to better maintain the sludge temperature andfluidity. Once the chemicals are introduced and blended into the heatedsludge 18, a first chemically-treated sludge 202 exits the last chemicalinjection mixer 140 b and is subsequently transferred to the decanterskid 114 to separate the high density solids out of the firstchemically-treated sludge 202. It should be noted that additionalchemical injection mixers may be added to the first chemical skid 118for the introduction of additional chemicals into the sludge 18.

Depending upon the particular initial sludge 14 composition, a widevariety of chemicals may be introduced and blended into the sludge 18 inorder facilitate subsequent processing to separate the solids out of thefirst chemically-treated sludge 202. Suitable chemicals include acids,demulsifiers, wetting agents, surfactants, flocculants, and defoamers.In one example, as the heated sludge 18 travels through the firstinjection mixer 140 a, the mixer 140 a injects an acid and blends theacid with the sludge 18 therein in order to neutralize adsorbed ionspresent at the interfacial emulsion film of the sludge 18. Subsequently,the sludge 18 is directed through the second injection mixer 140 bwherein a wetting agent is injected and blended into the sludge to alterthe affinity of the solids towards the water phase. It should be notedthat the present invention is not intended to be limited to the use ofany particular chemicals, and other chemicals may be substituted for anyof the aforementioned chemicals.

The first chemically-treated sludge 202 is directed to the decanter skid114 for solids removal. The chemically-treated sludge 202 entering thedecanter skid 114 can have a solids content as high as in the range of 6vol. % to 15 vol. %. As previously described, the decanter skid 114includes a decanter centrifuge 154 and a heating tank 156 mountedthereon and within the confines of the area of the skid 114. Thedecanter centrifuge 154 is used to reduce the solids content in thesludge 202 to a solids concentration less than about 2 vol. %. In thedecanter centrifuge 154, centrifugal force causes solids 204 to separateout of the sludge 202 and coalesce for subsequent removal from thedecanter through a solids outlet located in the bottom of the decantercentrifuge 154. A decanter-processed sludge 206 that exits the decantercentrifuge 154 has a solids content of less than about 2 vol. %. Aspreviously described, suitable decanter centrifuges include decantercentrifuges having a rotational speed of 3000 rpm or greater.

After reducing the solids in the sludge 206, the decanter-processedsludge 206 is transferred to the heating tank 156 and optionally heatedtherein. Because a significant amount of cooling can occur during theprevious processing steps since being heated in the heat exchanger 1301the decanter processed sludge 206 may be heated to a desired temperaturein the heating tank 156 in order to lower its viscosity and facilitateblending of additional chemicals into the sludge 206 during the nextprocessing step at the second chemical skid 120. After heating, a heateddecanter-processed sludge 208 is pumped via the second transfer pump 158to the second chemical skid 120. In one example, the heateddecanter-processed sludge 208 is heated to a temperature in the rangefrom about 65° C. to about 85° C.

The heated decanter-processed sludge 208 is transferred to the secondchemical skid 120 for chemically altering the sludge 208 to furtherbreak up the emulsion and promote phase separation. The chemical skid120 includes a plurality of chemical injection mixers 140 c, 140 d andchemical supply tanks 142 c, 142 d mounted thereon and within theconfines of the area of the skid 120 so as to maintain the portabilityof the skid 120, Chemical addition is typically required to furtherdestabilize the emulsion and change such properties to enhanceoil-water-solids phase separation during the next processing steps atthe phase separator skid 110. Each of the chemical injection mixers 140c, 140 d includes a static shear mixer having an injection point forintroducing a chemical into the sludge 208. As illustrated in FIG. 6,two chemicals are added to the sludge 208 as the sludge travels throughmixers 140 c, 140 d. Chemical supply tanks 142 c, 142 d store thechemicals until they are transferred via chemical lines 144 c, 144 d tothe mixers 140 c, 140 d. Preferably at least one dosing pump (not shown)in fluid communication with each of the chemical injection mixers 140 c,140 d is used to provide a predetermined quantity of chemical to theinjection point of the mixer for introduction into the sludge 208. Inaddition, the chemical injection mixers 140 c, 140 d are preferablyinsulated to better maintain the sludge temperature and fluidity. Oncethe chemicals are introduced and blended into the sludge 208, a secondchemically-treated sludge 210 exits the last chemical injection mixer140 d and is subsequently transferred to the phase separator skid 110.It should be noted that additional chemical injection mixers may beadded to the second chemical skid 120 for the introduction of additionalchemicals into the sludge 208.

Depending upon the particular sludge 208 composition, a wide variety ofchemicals may be introduced and blended into the sludge to promoteseparation of the water, oil, and solid phases of the secondchemically-treated sludge 210. Suitable chemicals include acids,demulsifiers, wetting agents, surfactants, flocculants, and defoamers.In one example, as the sludge 208 travels through the third injectionmixer 140 c, the mixer 140 c injects a demulsifier into the sludge 208to break the interfacial emulsion film to release the secondary waterphase. Afterwards, the sludge 208 is directed through the fourthinjection mixer 140 d wherein a defoamer is injected and blended intothe sludge for the purpose of preventing foaming. Again, it should benoted that the present invention is not intended to be limited to theuse of any particular chemicals, and other chemicals may be substitutedfor any of the aforementioned chemicals. Furthermore, additionalchemical injection mixers may be added to the second chemical skid 120for the introduction of additional chemicals into the sludge 208.

After the second chemical treatment, the sludge 210 is directed to thephase separator skid 11 for separating water and solids from the oilphase of the sludge 210. As previously described, the phase separatorskid 110 includes a surge tank 146 and a three-phase separator 148mounted thereon. The sludge 210 is fed into the vertically-orientedsurge tank 146 which separates solids from the sludge 210 and provides acontinuous flow of a liquid portion of the sludge 212 to the three-phaseseparator 148. Separated solids 214 that settle and accumulate in abottom region of the surge tank 146 are discharged to the solidsreceiving tank 150. The liquid portion of the sludge 212 which comprisesoil, water, gas, and fine solids is directed to the three-phaseseparator 148.

The liquid portion of the sludge 212 flows into the three-phaseseparator 148 through an inlet located at one end of the separator 148.After phase separation within the retention section of the three-phaseseparator 148, a water-rich phase 218 is discharged to a water tank 152,an oil-rich phase 220 is transferred to the oil purification skid 116,and a gas phase 228 is directed to the gas purification skid 112. Anysolids 216 that may settle out of the sludge 212 and accumulate in abottom region of the separator 148 during separation of the phases aredischarged to the solids receiving tank 150.

The oil-rich phase 220 is transferred to the oil purification skid 116for final purification and recovery of oil therefrom having a BS&W ofless than about 1 vol. %. As previously described, the oil purificationskid 116 includes a disk stack centrifuge 160 mounted thereon. Theoil-rich phase 220 is fed into the disk stack centrifuge 160 whereinextremely high centrifugal forces separate the very fine water emulsionand the ultra-fine solids out of the oil-rich phase 220. After phaseseparation, a water stream 222, a recovered oil stream 224, and anultra-fine solids phase 226 are discharged from the centrifuge 160. Therecovered oil stream 224 has a BS&W less than about 1 vol. % and iscommercially marketable.

The gas phase 228 is transferred to the gas purification skid 112 wherethe gas phase 228 is treated to remove VOCs prior to discharge into theenvironment. As previously described, the gas purification skid 112preferably includes a free water knockout pot 162, at least one mistimpinger 166, and at least one activated carbon filter 168 mountedthereon. A VFD-controlled vacuum blower 164 attached to the knockout pot162 is used to draw the gas phase 228 from a gas vent located in anupper side of the three-phase separator 148 through the knockout pot 162filled with water. Hydrocarbons in the gas phase 228 adhere to the wateras the gas travels upwardly through the pot 162. A wet-gas 230 thatexits a gas outlet near the top of the knockout pot 162 is directedthrough at least one mist impinger 166 to remove water from the gas 230and provide a dry gas 232. The dry gas 232 is transferred to anactivated carbon filter 168 to remove contaminants (e.g., remainingVOCs) therefrom in order to ensure a gas 234 that meets the regulatorystandards for release to the atmosphere.

According to still another embodiment of the invention, FIG. 3 depictsthe skid arrangement of a modular apparatus 300 optimally configured forrecovering the valuable hydrocarbon component of sludge 14 initiallyhaving a low concentration of solids. In FIG. 3 the same referencenumerals are used to indicate the same skids as those previouslydescribed with respect to the apparatus 100 depicted in FIG. 1. Modularapparatus 300 comprises the pumping skid 102, the shaker skid 104, theheating skid 106, the chemical skid 108, the phase separator skid 110,the gas purification skid 112, and the oil purification skid 116. Thisembodiment excludes the use of the decanter skid 114. For sludge 14initially having a low concentration of solids, it may be unnecessary toinclude a decanter centrifuge for the removal of solids.

Illustrated in FIGS. 4 and 7, modular apparatus 300 processes pit sludgethrough the pumping skid 102, the shaker skid 104, the heating skid 106,the chemical skid 108, the phase separator skid 110 the gas purificationskid 112, and the oil purification skid 116. As previously describedwith respect to FIG. 4, the modular apparatus 300 processes pit sludge10 through the pumping skid 102, the shaker skid 104, and the heatingskid 106 to provide a heated sludge 18.

Referring now to FIG. 7, the heated sludge 18 is transferred to thechemical skid 108 for chemically altering the sludge 18 to break up theemulsion and promote phase separation. In FIG. 7 the same referencenumerals are used to indicate the same features as those previouslydescribed with respect to apparatus 100 depicted in FIG. 5. Aspreviously described, the chemical skid 108 includes a plurality ofchemical injection mixers 140 a-d and chemical supply tanks 142 a-dmounted thereon. Chemical addition is typically required to destabilizethe emulsion and change such properties of the sludge 18 to enhance theits phase separation during the next processing step at the phaseseparator skid 110. As previously described, each of the chemicalinjection mixers 140 a-d includes a static shear mixer having aninjection point for introducing a chemical into the sludge 18 while themixer simultaneously blends the chemical and the sludge 18 under theshearing action of the mixer. As illustrated in FIG. 7, four chemicalsare added to the heated sludge 18 as the sludge is directed through thechemical injection mixers 140 a-d. Chemical supply tanks 142 a-d storethe chemicals until they are transferred via chemical lines 144 a-d tothe mixers 140 a-d for injection into the sludge 18. Preferably at leastone dosing pump (not shown) in fluid communication with each of thechemical injection mixers 140 a-d is used to provide a predeterminedquantity of chemical to the injection point of the mixer forintroduction into the sludge 18. Preferably, chemical injection mixers140 a-d are thermally insulated to better maintain the sludgetemperature and fluidity. Once the chemicals are introduced and blendedinto the heated sludge 18, a chemically-treated sludge 302 exits thelast chemical injection mixer 140 d and is subsequently transferred tothe phase separator skid 110 for separating the water, oil and solidphases of the sludge 302. Again, it should be noted that additionalchemical injection mixers may be added to the chemical skid 108 for theintroduction of additional chemicals into the sludge 18.

After chemical treatment, the sludge 302 is directed to the phaseseparator skid 110 for separating water and solids from the oil phase ofthe sludge 302. As previously described, the phase separator skid 110includes a surge tank 146 and a three-phase separator 148 mountedthereon. The sludge 302 is fed into the vertically-oriented surge tank146 which contains an interior plate that facilitates the small solidswithin the sludge to aggregate and form larger solids that settle out ofthe sludge 302 and accumulate in a bottom region of the surge tank 146.Separated solids 306 that accumulate in the surge tank 146 aredischarged to the solids receiving tank 150. The surge tank 146 alsoprovides a continuous flow of a liquid portion of the sludge 304 to thethree-phase separator 148 for oil, water, gas, and solid phaseseparation.

The liquid portion of the sludge 304 flows into the three-phaseseparator 148 through an inlet located at one end of the separator 148.After phase separation within the retention section of the three-phaseseparator 148, a water-rich phase 310 is discharged to a water tank 152,an oil-rich phase 312 is transferred to the oil purification skid 116,and a gas phase 320 is directed to the gas purification skid 112. Anysolids 308 that may settle out of the sludge 304 and accumulated in abottom region of the separator 148 during separation of the phases aredischarged to the solids receiving tank 150.

The oil-rich phase 312 is transferred to the oil purification skid 116for final purification and recovery of oil therefrom having a BS&W ofless than about 1 vol. %. As previously described, the oil purificationskid 116 includes a disk stack centrifuge 160 mounted thereon. Theoil-rich phase 312 is fed into the disk stack centrifuge 160 whereinextremely high centrifugal forces separate the very fine water emulsionand the ultra-fine solids out of the oil rich phase 312. After phaseseparation, a water stream 314, a recovered oil stream 316, and anultra-fine solids phase 318 are discharged from the centrifuge 160. Therecovered oil stream 316 has a BS&W less than about 1 vol. % and iscommercially marketable.

The gas phase 320 is transferred to the gas purification skid 112 wherethe gas phase 320 is treated to remove VOCs prior to discharge into theenvironment. As previously described, the gas purification skid 112preferably includes a free water knockout pot 162, at least one mistimpinger 166, and at least one activated carbon filter 168 mountedthereon. A VFD-controlled vacuum blower 164 attached to the knockout pot162 is used to draw the gas phase 320 from a gas vent located in anupper side of the three-phase separator 148 through the knockout pot 162filled with water. Hydrocarbons in the gas phase 320 adhere to the wateras the gas travels upwardly through the pot 162. A wet-gas 322 thatexits a gas outlet near the top of the knockout pot 162 is directedthrough at least one mist impinger 166 to remove water from the gas 322and provide a dry gas 324. The dry gas 324 is transferred to anactivated carbon filter 168 to remove contaminants (e.g., remainingVOCs) therefrom in order to ensure a gas 326 that meets the regulatorystandards for release to the atmosphere.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A modular apparatus for recovering oil from oil-based sludge,comprising: a pumping skid having a pump operable to homogenize anoil-based sludge; a shaker skid having a screen that removesparticulates from the oil-based sludge as the sludge traverses thescreen to form a debris-free sludge; a heating skid having a heatexchanger operable to heat the debris-free sludge as the debris-freesludge flows through the heat exchanger to form a heated sludge; achemical skid having at least one chemical injection mixer operable toinject a chemical into the heated sludge and mix the chemical with theheated sludge to form a chemically-treated sludge; a phase separatorskid having a three-phase separator operable to separate the phases ofthe chemically-treated sludge to form a first solids component stream afirst water component stream, a first oil component stream, and a firstgas component stream, a decanter skid having a decanter centrifugeoperable to remove solids from the first oil component stream to form asecond solids component stream and a second oil component stream; and anoil purification skid having a disk stack centrifuge operable to removewater and solids from the second oil component stream to form a thirdsolids component stream, a second water component stream, and a thirdoil component stream.
 2. The modular apparatus of claim 1, wherein thepump is a submersible pump operable to homogenize an oil-based sludgelocated inside a sludge pit and to pump the sludge out of the sludge pitto the shaker skid.
 3. The modular apparatus of claim 1, wherein theshaker skid further comprises a holding tank operable to accumulate andcontain the debris-free sludge for providing a steady state flow rate ofthe debris-free sludge to the heating skid.
 4. The modular apparatus ofclaim 1, wherein the phase separator skid further comprises a surge tankoperable to separate solids from the chemically-treated sludge.
 5. Themodular apparatus of claim 1, wherein the decanter skid furthercomprises a heating tank operable to accumulate and heat the second oilcomponent stream.
 6. The modular apparatus of claim 1 further comprisinga gas purification skid having at least: one piece of equipment selectedfrom the group consisting of a free water knockout pot and an activatedcarbon filter, operable to remove hydrocarbons from the first gascomponent stream.
 7. The modular apparatus of claim 1, wherein thesecond oil component stream has a BS&W of less than 2%.
 8. The modularapparatus of claim 1, wherein the third oil component stream has a BS&Wof less than 1%.
 9. A modular apparatus for recovering oil fromoil-based sludge, comprising: a pumping skid having a pump operable tohomogenize an oil-based sludge; a shaker skid having a screen thatremoves particulates from the oil-based sludge as the sludge traversesthe screen to form a debris-free sludge; a heating skid having a heatexchanger operable to heat the debris-free sludge as the debris-freesludge flows through the heat exchanger to from a heated sludge; a firstchemical skid having at least one chemical injection mixer operable toinject a chemical into the heated sludge and mix the chemical with theheated sludge to form a first chemically-treated sludge; a decanter skidhaving a decanter centrifuge operable to remove solids from the firstchemically-treated sludge to form a first solids component stream and adecanter-processed sludge; a second chemical skid having at least onechemical injection mixer operable to inject a chemical into thedecanter-processed sludge and mix the chemical with thedecanter-processed sludge to form a second chemically-treated sludge; aphase separator skid having a three-phase separator operable to separatethe phases of the second chemically-treated sludge to form a secondsolids component stream, a first water component stream, a first oilcomponent stream, and a first gas component stream, and an oilpurification skid having a disk stack centrifuge operable to removewater and solids from the first oil component stream to form a thirdsolids component stream, a second water component stream, and a secondoil component stream.
 10. The modular apparatus of claim 9, wherein thepump is a submersible pump operable to homogenize an oil-based sludgelocated inside a sludge pit and to pump the sludge out of the sludge pitto the shaker skid.
 11. The modular apparatus of claim 9, wherein theshaker skid further comprises a holding tank operable to accumulate andcontain the debris-free sludge for providing a steady state flow rate ofthe debris-free sludge to the heating skid.
 12. The modular apparatus ofclaim 9, wherein the decanter skid further comprises a heating tankoperable to accumulate and heat the decanter-processed sludge.
 13. Themodular apparatus of claim 9, wherein the phase separator skid furthercomprises a surge tank operable to separate solids from the secondchemically-treated sludge.
 14. The modular apparatus of claim 9, furthercomprising a gas purification skid having at least one piece ofequipment selected from the group consisting of a free water knockoutpot and an activated carbon filter operable to remove hydrocarbons fromthe first gas component stream.
 15. The modular apparatus of claim 9,wherein the decanter-processed sludge has a BS&W of less than 2%. 16.The modular apparatus of claim 9, wherein the second oil componentstream has a BS&W of less than 1%.
 17. A modular apparatus forrecovering oil from oil-based sludge, comprising: a pumping skid havinga pump operable to homogenize an oil-based sludge; a shaker skid havinga screen that: removes particulates from the oil-based sludge as thesludge traverses the screen to form a debris-free sludge; a heating skidhaving a heat exchanger operable to heat the debris-free sludge as thedebris-free sludge flows through the heat exchanger to form a heatedsludge; a chemical skid having at least one chemical injection mixeroperable to inject a chemical into the heated sludge and mix thechemical with the heated sludge to form a chemically-treated sludge; aphase separator skid having a three-phase separator operable to separatethe phases of the chemically-treated sludge to form a first solidscomponent stream, a first water component stream, a first oil componentstream, and a first gas component stream; and an oil purification skidhaving a disk stack centrifuge operable to remove water and solids fromthe first oil component stream to form a second solids component stream,a second water component stream, and a second oil component stream. 18.The modular apparatus of claim 17, wherein the pump is a submersiblepump operable to homogenize an oil-based sludge located inside a sludgepit and to pump the sludge out: of the sludge pit to the shaker skid.19. The modular apparatus of claim 17, wherein the shaker skid furthercomprises a holding tank operable to accumulate and contain thedebris-free sludge for providing a steady state flow rate of thedebris-free sludge to the heating skid.
 20. The modular apparatus ofclaim 17, wherein the phase separator skid further comprises a surgetank operable to separate solids from the chemically-treated sludge. 21.The modular apparatus of claim 17, further comprising a gas purificationskid having at least one piece of equipment selected from the groupconsisting of a free water knockout pot and an activated carbon filter,operable to remove hydrocarbons from the first gas component stream. 22.The modular apparatus of claim 17, wherein the first oil componentstream has a BS&W of less than 2%.
 23. The modular apparatus of claim17, wherein the second oil component stream has a BS&W of less than 1%.